Women have puzzled over it for years—why the heck do men do the things they do? Why do they profess their love for you one minute, then ignore you the next (say, when an Attila the Hun special turns up on TV)? Why can they not remember our birthdays? Let science explain some of these conundrums—and help you rev up your relationships!

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Be patient with his memory

The hippocampus, where initial memories are formed, occupies a smaller percent of the male brain than the female brain. If on your first date he can't remember where you work, even though you told him all about it when you met, just remember that size matters … hippocampus size, that is. Don't take it personally. (Oh, and don't be surprised when, months down the line, he has no clue you've just changed your hair.)

Don't expect him to get hints

Have a crush on him? You may have to put it out there, because men aren't as skilled at women at reading subtle emotional cues. As Dr. Larry Cahill of the University of California at Irvine puts it, "We have been assuming that the ways in which emotions are organized in the brain are essentially similar in men and women," but they aren't.

Parts of the limbic cortex, which is involved in emotional responses, are smaller in men than in women. Additionally, scientists at McMaster University have found that guys have a smaller density of neurons in areas of the temporal lobe that deal with language processing.

That's why it's probably a good idea to tell him straight-up how you're feeling ("I'm kind of hurt that you forgot I hate sushi"). Expecting him to infer from your hints could leave both of you scratching your heads.

Don't take conversation lulls personally

Fact is, guys in general just aren't as verbally adept as women are. Large parts of the cortex — the brain's outer layer that does a big part of recognizing and using subtle language cues — are thinner in men than they are in women.

A study led by Dr. Godfrey Pearlson of Johns Hopkins University has shown that two areas in the frontal and temporal lobes that play an important role in language processing are significantly smaller in men. Using MRIs, the Johns Hopkins scientists measured gray matter volumes in several brain regions in 17 females and 43 males.

Women had 23 percent more volume than men in the dorsolateral prefrontal cortex and 13 percent more volume than men in the superior temporal cortex. "Women," explains Dr. Cahill, "excel in being able to come up with appropriate words, given cues." Men — not so much. Don't expect him to chatter with you on dates with the skill of a girlfriend, and don't assume he's not interested in you if he occasionally lets the conversation lapse. Think of it this way: He's simply basking in moments of quiet companionship.

Appreciate his naturally upbeat nature

Does he seem to be "up" most of the time? It's not your imagination: Male brains produce 52 percent more serotonin (the chemical that influences mood) than female brains, according to a study done at McGill University. And studies show that fewer men than women suffer from depression. Guys may also have an easier time rolling with life's big stresses. If he tells you he recently lost his golden lab or suffered a job loss and doesn't get all teary, it doesn't mean he's heartless; rather, he has healthy stores of serotonin.

Don't expect his take on your relationship history to match yours

He may be incapable of seeing your shared past the way you do. Brain images have started to show that men and women use their brains in vastly different ways. For example, women use the left part of the amygdala — the part of the brain that creates emotional reactions to events — to put memories in order by emotional strength, meaning that something emotionally important to them (like a great first date a couple of months ago) will be ordered in front of what they ate for breakfast yesterday.

Men, however, use the right part of the amygdala to put memories in order. Traditionally, the right hemisphere of the brain is associated with the central action of an event, while the left hemisphere is associated with finer details. Translation: You'll both remember your first date, but he might not remember the color of your sweater or the light rain that was falling that night. It doesn't mean he was checked out; it just means he's a guy.

Remember his brain is his largest sex organ

In males of several species including humans, the preoptic area of the hypothalamus is greater in volume, in cross-sectional area and in the number of cells. In men, this area is more than two times larger than in women, and it contains twice as many cells. And what, say you, does this have to do with the horizontal mambo? Plenty. This area of the hypothalamus is in charge of mating behavior.

This small structure connects to the pituitary gland, which releases sex hormones. So if your bf wants to get intimate all the time and you feel like Ms. Low Desire, remember: You're just experiencing normal, brain-based differences.

Laura Schaefer is the author of Man with Farm Seeks Woman with Tractor: The Best and Worst Personal Ads of All Time. For the other side of this story, read The Female Brain, Explained.